The performance of many devices fabricated using semiconductor methods is critically dependent upon the three-dimensional (3D) structure thereof. For example, the performance of a perpendicular magnetic recording (PMR) write pole is highly dependent upon the 3D shape of the write pole near the air bearing surface (ABS), the nose length, and pole flare and/or pinching. To obtain information about the efficacy of manufacturing methods of these and other devices, it is desirable to measure the 3D structure of these devices when comparing the performance of different designs.
One approach to measuring the 3D structure of a device in a wafer involves a “slice and view” (SnV) method employing a dual beam Focused-Ion-Beam Scanning Electron Microscope (FIB/SEM). In this method, the dual beam FIB/SEM is employed to produce a series of cross-sectional views of the 3D structure. Successive cuts are made in the device, and a cut placement (CP) position is measured after each cut.
This may be more easily understood with reference to FIGS. 1a-1e, which illustrate the SnV approach to measuring the 3D structure of a PMR write pole. As can be seen with reference to FIG. 1a, several cuts are made using a dual beam FIB/SEM along different planes (i.e., A-A, B-B, C-C and D-D) intersecting the write pole 100. Each cut is made a different distance from a fiducial structure 101 of the write pole, whose position relative to the ABS is known a priori. In this regard, the cut made in plane A-A is a distance d1 from fiducial 101, the cut made in plane B-B is a distance d2 from fiducial 101, the cut made in plane C-C is a distance d3 from fiducial 101, and the cut made in plane D-D is a distance d4 from fiducial 101. Each of these cuts can provide a cross sectional view of write pole 100, as illustrated in FIGS. 1b-1e. In this regard, a cross-sectional view of write pole 100 in plane A-A is illustrated in FIG. 1b, a cross-sectional view of write pole 100 in plane B-B is illustrated in FIG. 1c, a cross-sectional view of write pole 100 in plane C-C is illustrated in FIG. 1d, a cross-sectional view of write pole 100 in plane D-D is illustrated in FIG. 1e. From these cross-sectional view of write pole 100, information regarding the 3D structure thereof can be determined.
Unfortunately, the foregoing SnV method can generate incorrect measurements in small devices in a wafer, such as PMR write poles, as each succeeding CP measurement may be distorted by the preceding cuts (e.g., the measurement of the CP may give inaccurate results as the relative distance between the fiducial and the new cut may have been changed by the intervening cuts).